A database is a collection of stored data that is logically related and that is accessible by one or more users or applications. A popular type of database is the relational database management system (RDBMS), which includes relational tables, also referred to as relations, made up of rows and columns (also referred to as tuples and attributes). Each row represents an occurrence of an entity defined by a table, with an entity being a person, place, thing, or other object about which the table contains information.
One of the goals of a database management system is to optimize the performance of queries for access and manipulation of data stored in the database. Given a target environment, an optimal query plan is selected, with the optimal query plan being the one with the lowest cost, e.g., response time, CPU processing, I/O processing, network processing, etc., as determined by an optimizer. The response time is the amount of time it takes to complete the execution of a query on a given system.
Counting the number of distinct values in several columns of a table is a common query. However, current parallel aggregation mechanisms do not handle this situation well and typically introduce unnecessary and hence inefficient processing during performance of such queries.
Therefore, what is needed is a mechanism that overcomes the described problems and limitations.